Because of their excellent features such as a small size, a reasonable price, and a high output, semiconductor lasers are used in many technical fields ranging from, for example, the IT technology such as communications and optical disks to the medical field to part of the illumination technology. Semiconductor light sources (semiconductor light emitting elements) having a wavelength of 450 nm to 540 nm and using GAN semiconductor lasers have been developed in recent years to be available for use in light sources of display devices such as a laser display and a backlight liquid crystal display (LCD).
It is important for the semiconductor light emitting elements used in these display devices to output a higher output of light to obtain a clear image. Moreover, reduction of power consumption is required to simplify and reduce the cost of a heat-dissipation mechanism of a display device and improve the reliability of the semiconductor light emitting element itself.
In a semiconductor light emitting element such as a semiconductor laser, a decrease of a threshold value can increase a light output obtained for the same injection current value, thereby achieving a higher light output and a lower current. This can reduce power consumed by the semiconductor light emitting element.
To increase a parameter called vertical optical confinement factor (Γv) is known as a way to decrease a threshold value in the semiconductor laser. Moreover, in many cases, InGaN or GaN is used for a light guide layer and AlGaN having a lower refractive index than InGaN and GaN is used for a clad layer, in a group III nitride semiconductor laser using a general n-type GaN substrate.
To lower the refractive index of the clad layer to improve the vertical optical confinement factor (Γv), use of AlInN having a very low refractive index for the n-type clad layer is disclosed, for example (non patent literature 1 (NPL 1)). Moreover, a test was conducted in which n-GaN layers were regularly formed in an AlInN layer and electricity was conducted in a stacking direction of layers (non patent literature 2 (NPL 2)).